The influence of AlN nucleation layer on RF transmission loss of GaN buffer on high resistivity Si (111) substrate

A sufficiently low transmission loss in radio frequency (RF) is one of the critical requirements for GaN-on-Si RF devices to achieve high performance. We have systematically studied the mechanism and effect of the AlN nucleation layer on the RF loss of the GaN-on-Si device buffer stack. Our results show that the RF loss is strongly influenced by the growth parameters of the AlN nucleation layer during epitaxial process. It is observed that the AlN nucleation layer grown at a low thermal budget with a low density of deep surface pits can efficiently reduce the AlN/Si interface loss by suppressing the conductive channel at AlN/Si interface which is governed largely by the thermal diffusion of Al and Ga into the Si substrate. By optimizing the growth process of the AlN nucleation layer, the RF loss of the GaN-on-Si device buffer can be dramatically reduced by up to similar to 40%.